The invention relates to a process making it possible to ensure the filling of drums containing dangerous wastes, such as very low level radioactive waste, previously processed and compacted to form xe2x80x9cflat cakesxe2x80x9d piled on top of each other inside the drum.
Another object of the invention is an installation for operating this process.
In nuclear installations, low level technological wastes are first of all processed in cylindrical metallic containers. The volume of these containers is, for example, 120 litres.
The containers holding the wastes are then compacted using a press, to obtain xe2x80x9ccakesxe2x80x9d greatly reduced in volume, height-wise relative to the containers.
During a later stage, these cakes are piled in cylindrical metal drums. As a general rule, five cakes, for example, are piled in each of the drums.
During a following operation called xe2x80x9cblockingxe2x80x9d the drums are placed on a vibrating table and filled with a blocking material such as a cement plaster or grout.
When a drum has been filled with blocking material, it is then closed by means of a crimped lid.
Finally, when the blocking material is dry, the drums are transported to a long-term surface storage site.
More precisely, the invention concerns the blocking operation, during which the drums containing the cakes are filled with a blocking material.
At the time of this operation, which is carried out in a workshop, the contaminated air contained in the drum escapes into the workshop and tends, in particular, to contaminate the external wall of the drum as well as the close surroundings. In fact, a volume of contaminated air equivalent to that of the blocking material injected into the drum escapes from it to the outside.
In prior art, no known technical solution exists for this problem.
The object of the invention is precisely a process for filling a drum containing dangerous wastes, making it possible to avoid any dispersion of contamination into the atmosphere of the room, and in particular onto the external wall of the drum, due to the contaminated air ejected from the drum during the blocking operation.
According to the invention, this result is obtained by means of a process for filling drums containing dangerous wastes, characterised in that it comprises the following stages:
assembly of an intermediary lid on a drum, said lid comprising an opening closed in a sealed fashion by a cap;
perforation of the cap by a toothed crown carried by a containment hood overhanging an end of the drum closed by the intermediary lid;
injection of a blocking material into the drum, by means of an injection tube located inside the toothed crown;
negative pressure application to the drum and the containment hood, as soon as the drum is set in place and during perforation and injection.
In the process described above, the intermediary lid provided with its cap ensures the sealed containment of the drum before perforation of the cap. After perforation, dynamic containment is ensured by negative pressure application to the drum and containment hood. Thus, the contaminated air contained in the drum is sucked out as the drum is filled with the blocking material, without this air being dispersed into the atmosphere of the workshop. Thus one avoids in particular, any contamination of the external walls of the drum.
According to a preferred embodiment of the invention, the end of the filling of the drum by blocking material is detected, in such a way as to stop injection of this material.
Detection of the end of filling of the drum can in particular be ensured by at least one bubble tube opening into the interior of the toothed crown.
In this case, in order that the level of filling can be controlled with precision, advantageously the end of the bubble tube is positioned at a predetermined level below the cap, after perforation of the latter. To do this, one can in particular use a laser detector mounted on the containment hood and able to measure the distance between the latter and the intermediary lid.
Preferably, the cap is equipped with ballast means to ensure, through gravity, the evacuation into the drum of the disc cut out in the cap by the toothed crown, in order to avoid total or partial closing of the orifice of the injection tube through a suction effect on the cap.
The perforation of the cap can in particular be carried out by displacing the drum upwards relative to the fixed containment hood. Advantageously, lifting means such as a jack can be used for this. Preferably, these lifting means are associated with means capable of making the drum they support vibrate, during filling, so as to improve the penetration of the blocking material in the drum, around the radioactive waste.
As a variant, the perforation of the cap can also be obtained by displacing the toothed crown or the hood downwards.
In order to avoid in particular the blocking material setting before being injected into the drum, advantageously this material is made to circulate continuously in a closed circuit, during the period preceding this injection.
Moreover, after injection of the blocking material into the drum, it is preferable to carry out a cleaning of the means of injection, that is to say of the closed circuit and the nozzle through which the material is injected into the drum.
Finally, after injection of the blocking material into the drum, the latter is separated from the containment hood and an external lid is placed on the drum, above the intermediary lid. The drum then passes into a crimping machine which crimps the external lid. Then the drum is in a condition ready for storage, before being transported to a site prepared for very long-term storage.
Another object of the invention is an installation for filling drums containing dangerous wastes, characterised in that it comprises:
an intermediary lid able to be mounted on a drum, said lid comprising an opening closed in a sealed fashion by a cap;
a containment hood able to overhang an end of the drum closed by the intermediary lid, said hood having a toothed crown able to perforate the cap;
means of injection of a blocking material, opening inside the toothed crown; and
means of negative pressure application for the drum and the containment hood.